1. Field of the Invention
The invention relates to a control device for a hybrid vehicle including a power split mechanism, and particularly to a technique for reducing rattling noise resulting from the rotational fluctuations of an engine.
2. Description of Related Art
A hybrid vehicle has been widely available which includes a differential mechanism that splits power from an engine to a first motor generator (MG) and an output-side rotating member, and a second MG connected to the output-side rotating member to be capable of transmitting the power. In such a hybrid vehicle, vibration due to the rotational fluctuations of an engine resulting from the torque fluctuations of the engine is transmitted to the meshing portions of a gear pair. As a result, in the meshing portions, the tooth surfaces of the meshing teeth strike each other by repeatedly colliding with and separating from each other. This may cause rattling noise referred to as a so-called rattling sound. It is disclosed in Japanese Patent Application Publication No. 2003-314614 (JP 2003-314614 A) that, to reduce such a rattling sound, a dynamic damper is configured by connecting a motor (corresponding to the foregoing second MG) to a rotation element to which the power of an engine is transmitted via a spring and, using the inertia of the motor in combination with the spring, torsional resonance vibration is reduced. It is also disclosed in each of Japanese Patent Application Publication No. 2004-23985 (JP 2004-23985) and Japanese Patent Application Publication No. 2008-201351 (JP 2008-201351 A) that, to reduce the rattling sound, rattling sound suppression control (synonymous with rattling noise suppression control) which changes the operating point of an engine is executed.